1. Field of the Invention
The present invention relates to improved catalysts for the treatment of exhaust gases from internal combustion engines, and, more especially, to the preparation of such catalysts for the treatment of exhaust gases from internal combustion engines, which catalysts effect not only the oxidation of carbon monoxide and of the hydrocarbons present in said exhaust gases, but also, optionally simultaneously, the reduction of the nitrogen oxides present in these gases.
2. Description of the Prior Art
In general, the catalysts suitable for the catalytic oxidation and optionally for the catalytic reduction of the constituents present in the exhaust gases from internal combustion engines comprise a support or carrier which is coated and/or impregnated with at least one precious metal from the platinum group, such as platinum, rhodium, ruthenium, palladium or iridium, and at least one base metal, these base metals typically being selected from among: cobalt, zinc, manganese, nickel, tungsten, cerium, iron, copper, neodymium, praseodymium, rhenium, yttrium, magnesium, chromium, zirconium, molybdenum, lanthanum, tin, calcium, strontium and barium.
Such catalysts are typically prepared by the common methods either by impregnation of the support or by the introduction of the metals of the active phase during the manufacture or production of the support. In general, this is done by impregnation of the support with solutions of inorganic or organic compounds of the metals sought to be introduced.
Thus, according to published European patent application No. 27,069, assigned to the assignee hereof, it is known to produce three-way catalysts for the treatment of exhaust gases from internal combustion engines by successive impregnation of the support with a solution containing compounds of iron and of cerium, and then with a solution containing the compounds of the precious metals of the platinum group sought to be incorporated therein. Cf. U.S. Pat. No. 4,378,307, also assigned to the assignee hereof.